Hi everybody. A couple of days ago I started downloading the 3.1 DVD. I've just finished the first one which had this jigdo filename: debian-31r0-i386-binary-1.jigdo.
So 2 days later I'm starting to download the 2nd dvd, but the jigdo file name has changed:
debian-31r0a-i386-binary-2.jigdo. I suppose this has to do with the security issue that the updates had not been turned on? But more importantly, will the new image of the second disc work flawlessly with the first one (the non 31r0a)? I hope I was not downloading the image in vain!

If you are on a speedy internet connection, all you need is Disk 1 - you can do the rest online.

Take a look at what's written at the top of this page: http://cdimage.debian.org/debian-cd/3.1_r0a/
In short words, the 3.1_r0 images were found to have a bug regarding the sources.list file. That's why the 3.1_r0a came up, but there's no problem in using the "non-a" image, except for a small modification you have to do manually.